Fighter airplanes often operate under high g conditions, often under circumstances where the onset of the high g condition occurs very rapidly. Current high-performance airplanes, such as the F-15 and F-16, are capable of sustaining g forces in excess of +9 g; and the "g-onset," i.e., the rate of increase in the acceleration forces, can exceed 6 g/second. These high g and high g-onset conditions can cause a reduction in the performance of a pilot and can result in fatigue, loss of peripheral vision, and potential loss of consciousness. It is expected that future fighter airplanes will be capable of sustaining even higher g forces, possibly as high 13-15 g. Yet existing anti-g protective measures, such as positive pressure breathing, anti-g suits, and rapid response g-valves, are generally able to allow pilots to sustain only about 7 g.
Although much air-to-air combat occurs between aircraft at great distances from each other, the ability to engage in close air-to-air combat, i.e., "dog fights," is nevertheless a critical requirement of high-performance fighter aircraft. When engaging in a dog fight, it is necessary for the pilot to frequently check the rear or "six-o'clock" position in order to be sure that an enemy aircraft is not behind the aircraft. The pilot will normally move one shoulder forwardly to rotate his torso in one direction and then rotate his head the remaining distance in the same direction in order to check the six-o'clock position. However, it can be extremely difficult for the pilot to rotate his head and body under high g forces thus making a pilot less able to check the 6-o'clock position.
In order to allow pilots to sustain g forces in the neighborhood of 9-15 g, it is necessary to place the pilot in a reclined position. However, permanently placing the pilot in a reclined position can reduce the pilot's visibility and otherwise impair the performance of the pilot. Consequently, articulating or reclining seats have been proposed in which the seats are normally placed in an upright position under low g conditions. However, when the g forces reach a predetermined value, such as in excess of 7 g, the seat automatically articulates or reclines to angles of 50.degree.-65.degree. to provide the needed protection. It is expected that articulating or reclining seats will thus allow the pilot to sustain g forces as great as 13-15 g.
When the pilot is reclining under high g conditions, the pilot must still have the ability to check the six-o'clock position, yet it is even more difficult for the pilot to check the 6 o'clock position when he is in a reclined position since the pilot must now lift his chest and one shoulder. Yet the weight of his chest and shoulder has greatly increased because the g forces are acting in a direction that forces his torso against the seat back.
Prior attempts to assist the pilot in checking the six-o'clock position under high g conditions have relied upon mechanical movement of the seat back. This approach adds weight to the seat and, because of its complexity, decreases the reliability and maintainability of the system.